Heretofore, a level sensor having a plurality of light receiving elements arranged up and down in parallel has been known. For example, see Japanese Patent Application Publication No. 2004-309440.
Such a level sensor amplifies received light signals outputted from the light receiving elements with respective multiple amplifiers, compares signals outputted from the amplifiers with a threshold using respective multiple comparators, and obtains a level, i.e., the center position of a laser beam, based on a comparison signal outputted from each comparator.
In such level sensor, an amplifier and a comparator should be arranged for each light receiving element, thus increasing the circuit complexity and cost.
Accordingly, there is a need for a level sensor with which a light receiving position of a laser beam can be obtained by just providing a simple circuit.